Pop-up origami robots inspired by children's books

Harvard engineers have developed a way to create swarms of 'pop-up' robots to be printed out by the sheet.

To make them, they laminate together 18 layers of carbon fiber, a plastic fim called Kapton, titanium, brass, ceramic, and adhesive sheets in a complex, laser-cut design.

The structure incorporates flexible hinges, so that the three-dimensional product — just 2.4 millimeters tall — can be assembled in one movement, like a pop-up book.

"This takes what is a craft, an artisanal process, and transforms it for automated mass production," says Pratheev Sreetharan, who co-developed the technique with J Peter Whitney.

The Harvard team has been working for years to create bio-inspired, bee-sized robots that can fly and behave autonomously as a colony. Until now, though, they've been using a fiddly and error-prone method to fold, align, and secure each of the minuscule parts and joints.

"You'd take a very fine tungsten wire and dip it in a little bit of superglue," sayss Sreetharan. "Then, with that tiny ball of glue, you'd go in under a microscope like an arthroscopic surgeon and try to stick it in the right place."

Now, though, they're achieving the same result, without human error, through locking mechanisms and dip soldering. The new process also allows them to use cured carbon fiber, which is rigid and easy to align, rather than uncured carbon fiber, which Sreetharan compares to wet tissue paper.

"Our new techniques allow us to use any material including polymers, metals, ceramics, and composites," says principal investigator Rob Wood.

"The ability to incorporate any type and number of material layers, along with integrated electronics, means that we can generate full systems in any three-dimensional shape. We've also demonstrated that we can create self-assembling devices by including pre-stressed materials."

The technique has applications that go way beyond flying robots. It could be used for high-power switching, optical systems, and other tightly integrated electromechanical devices that have parts on the scale of micrometers to centimeters.

Indeed, the layering process builds on the manufacturing process currently used to make printed circuit boards, which means that the tools for creating large sheets of pop-up devices are common and abundant.

It also makes it easy to integrate electrical components such as sensors and control actuators.

Once a design's been produced, fabrication can be fully automated, with accuracy and precision limited only by the machining tools and materials.

"The alignment is now better than we can currently measure," says Sreetharan. "I've verified it to better than 5 microns everywhere, and we've gone from a 15% yield to — well, I don't think I've ever had a failure."